1. Field of the Invention
The present invention relates to an optical communication apparatus, and more specifically to an integral transmitter-receiver optical communication apparatus which is commonly used for both transmitting and receiving signals in the form of a laser beam modulated in accordance with an information signal, and further relates to a crosstalk preventive device for such an optical communication apparatus.
2. Description of the Related Art
FIG. 24 shows an integral transmitter-receiver optical communication apparatus as an example to which the present invention is applicable. This optical communication apparatus includes a telescopic optical system 10, a deflection mirror 20 and a transmitter-receiver unit 30. The telescopic optical system 10 is used for both projecting and receiving a laser beam modulated by an information signal. In this illustrated example, the telescopic optical system 10 is constructed as a reflecting telescope. The deflection mirror 20 is positioned between the telescopic optical system 10 and the transmitter-receiver unit 30 to adjust the direction of the receiving light which enters the transmitter-receiver unit 30 through the telescopic optical system 10 and also the direction of the transmitting light which is emitted from the transmitter-receiver unit 30 to the telescopic optical system 10.
The transmitter-receiver unit 30 is provided with a semiconductor laser source 32 which emits a laser beam modulated by the modulator 31 in accordance with the transmission information signal. The semiconductor laser source 32 is constructed to emit the modulated laser beam so that S-polarized light thereof is reflected. The transmitter-receiver unit 30 is further provided with a polarization beam splitter (PBS) 33 on which the linearly polarized light emitted from the semiconductor laser source 32 is incident. The polarization beam splitter 33 reflects S-polarized light while allowing P-polarized light to pass therethrough. The S-polarized light that is reflected by the polarization beam splitter 33 is incident on the deflection mirror 20 via a xcex/4 retardation plate 34. The transmitter-receiver unit 30 is further provided, on a transmission light path of the polarization beam splitter 33, with a beam splitter 35 in order to receive the light signal transmitted from a complementing optical transmitter, which is positioned opposite to the optical communication apparatus. A light receiving element 36 and a position detecting sensor 37, each of which receives a modulated laser beam, are respectively positioned on two separate light paths split by the beam splitter 35. Accordingly, the light emitted by the aforementioned complementing optical transmitter to be received by the telescopic optical system 10 is turned into P-polarized light through the xcex/4 retardation plate 34. Subsequently, the P-polarized light passes through the polarization beam splitter 33 and then enters the beam splitter 35 to be split into two separate light beams so that the two separate light beams are incident on the light receiving element 36 and the position detecting sensor 37, respectively. A signal processing circuit 38 is connected to the light receiving element 36 to read out the information conveyed by the light received by the light receiving element 36.
The integral transmitter-receiver optical communication apparatus having the aforementioned structure is generally positioned opposite to the semiconductor laser beam of a complementing optical communication apparatus having an identical structure, wherein the transmission range of the laser beam emitted by the semiconductor laser beam 32 overlaps the transmission range of the semiconductor laser beam emitted by the complementing optical communication apparatus, so that the laser beam modulated by the modulator 31 can be received by the light receiving element 36 in each of the mutually complementing optical communication apparatuses.
In each of the mutually complementing communication apparatuses, the deflection mirror 20 maintains the parallelism of the transmitting laser beam which is incident thereon to be deflected outwards through the telescopic optical system 10, and also the parallelism of the receiving laser beam which is emitted by the complementing optical communication apparatus to be incident on the deflection mirror 20. The deflection mirror 20 can include a rotatable deflection mirror which can be driven about two axes (X and Y axes) which are orthogonal to each other. A rotational portion of the rotatable deflection mirror is coupled to an electromagnetic driver which includes coils and permanent magnets. This electromagnetic driver is driven in accordance with signals output from the position detecting sensor 37. The position detecting sensor 37 detects the variation in the position of the receiving light which enters the transmitter-receiver unit 30 to output a drive command signal to the electromagnetic driver through a control circuit 21 and an X/Y driver 22 to rotate the deflection mirror 20 about the X-axis and the Y-axis thereof, so that the receiving light enters the transmitter-receiver unit at an appropriate position. The position of the deflection mirror 20 continues to be detected by the position detecting sensor 37 in a feed-back operation so that the parallelism of both the light transmitted by the transmitter and the light received by the receiver are maintained.
It is preferable in this type of integral transmitter-receiver optical communication apparatus that the magnification of the telescopic optical system (afocal optical system) 10 be small in order to prevent the image quality from deteriorating due to off-axis incident rays. However, it is preferable that the magnification of the telescopic optical system (afocal optical system) 10 be large in order to miniaturize the drive system for the deflection mirror 20 while miniaturizing the deflection mirror 20 and the following optical system after the deflection mirror 20. Furthermore, it is preferable that the intensity distribution of the transmission light be as close to a circular shape in cross section as closely as possible. It is also preferable that the diameter of the circular cross section (beam diameter) be adjustable.
Upon installation of the integral transmitter-receiver optical communication apparatus, a complementing apparatus which is identical thereto is also installed, so that these mutually complementing apparatuses are fixed at a predetermined distance apart from each other (e.g., one kilometer), and subsequently the direction of light transmitted by one of the mutually complementing apparatuses to the other must be finely adjusted, wherein the optical communication apparatus transmits signals (modulated laser beam) towards the complementing optical communication apparatus which receives the transmitted signals. In such an adjusting operation, not only is the beam diameter of the transmitting laser beam preferably adjustable, but also the peripheral edge of a cross section of the transmitting laser beam is preferably sharp.
In the conceptual structure of the integral transmitter-receiver optical communication apparatus shown in FIG. 24, crosstalk does not occur, in theory, between the transmitting laser beam emitted from the semiconductor laser source 32 and the received laser beam incident upon the light receiving element 36 and the position detecting sensor 37. However, in practice, there is a possibility of such crosstalk occurring due to the polarization beam splitter 33 not being able to perfectly polarize the incident light (in fact, it is practically impossible to provide a polarization beam splitter having a polarization beam splitting thin layer therein through which the incident light is perfectly polarized, and hence, the occurrence of a small percentage of infiltrating (stray) light cannot be prevented), and/or due to the polarization beam splitter 33 and the beam splitter 35 being positioned very closely to each other.
The first object of the present invention is to provide an integral transmitter-receiver optical communication apparatus having superior cost-performance without requiring excessive high quality, wherein the light deflecting optical system and the following optical systems provided after the light deflecting optical system can be miniaturized without deteriorating the image quality.
The second object of the present invention is to provide an integral transmitter-receiver optical communication apparatus in which the peripheral edge of a cross section of the transmitting laser beam can be made sharp.
The third object of the present invention is to provide an integral transmitter-receiver optical communication apparatus, wherein the occurrence of crosstalk between the transmitting light and the receiving light can be prevented in the case where a polarization beam splitting plane and a beam splitting plane are positioned adjacent to each other.
Other objects of the present invention will become apparent from the detailed description to follow taken in conjunction with the appended claims.
To achieve the object mentioned above, according to the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated in accordance with a transmission information signal, a receiver having a position detecting sensor and a light receiving element each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source, and for receiving the complementing modulated laser beam transmitted from the complementing transmitter, the telescopic optical system including a first afocal optical system; a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor, and the light beam deflecting device includes a deflection mirror; and a second afocal optical system positioned between the deflection mirror and the transmitter-receiver device. The first afocal optical system can decrease the beam diameter of a laser beam when the first afocal optical system is moved in a direction from the object side to the deflection mirror, and the second afocal optical system can decrease the beam diameter of a laser beam when the second afocal optical system is moved in a direction from the deflection mirror to the transmitter-receiver device. The following condition is also satisfied: m less than 2(xcex83/xcex81); wherein xe2x80x9cmxe2x80x9d represents the magnification of the first afocal optical system, xe2x80x9cxcex81xe2x80x9d represents the maximum off-axis incident angle of an incident ray on the first afocal optical system, and xe2x80x9cxcex83xe2x80x9d represents the maximum angle of rotation of the deflection mirror.
Preferably, the magnification of the second afocal optical system is equal to, or less than, half of the magnification of the first afocal optical system.
The deflection mirror can include a single deflection mirror which can be driven about two axes which are orthogonal to each other.
Alternatively, the deflection mirror can include two deflection mirrors which are driven about two orthogonal axes, respectively.
Preferably, the magnification of the second afocal optical system is less than the magnification of the first afocal optical system.
Preferably, the beam splitting device includes a polarization beam splitting plane and a beam splitting plane.
According to another aspect of the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal, a receiver having a position detecting sensor and a light receiving element each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter, the telescopic optical system including a first afocal optical system; a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor; a second afocal optical system positioned between the light beam deflecting device and the transmitter-receiver device; and a shaping optical system, positioned between the laser source and the light beam deflecting device, for forming the laser beam emitted from the laser source into a substantially circular cross section. The first afocal optical system includes a positive lens group and a negative lens group to decrease the beam diameter of a laser beam from the object side to the light beam deflecting device, and the second afocal optical system includes a positive lens group and a negative lens group to decrease the beam diameter of a laser beam from the light beam deflecting device to the transmitter-receiver device. Furthermore, at least one of the positive lens group or the negative lens group of the second afocal optical system is movable along an optical axis thereof.
Preferably, a laser beam traveling between the first afocal optical system and the second afocal optical system is a substantially parallel beam.
Preferably, a substantially parallel beam passes through the beam splitting device.
Preferably, a device for moving the laser source along an optical axis is further included to adjust a ratio of a length in a xcex8-parallel direction and a length in a xcex8-perpendicular direction of the intensity distribution of the laser beam emitted from the laser source in accordance with the beam-changing characteristics of the shaping optical system, the laser source moving device being used when the integral transmitter-receiver optical communication apparatus is assembled.
Preferably, the shaping optical system is positioned between the laser source and the second afocal optical system.
Preferably, the shaping optical system includes a collimating lens and an anamorphic optical system.
Preferably, the anamorphic optical system includes at least two prisms.
According to another aspect of the present invention, there is provided, an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source, and for receiving the complementing modulated laser beam transmitted from the complementing transmitter, the telescopic optical system including a first afocal optical system; a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor; and a second afocal optical system positioned between the light beam deflecting device and the transmitter-receiver device. The first afocal optical system can decrease the beam diameter of a laser beam when the first afocal optical system is moved in a direction from the object side to the light beam deflecting device. The second afocal optical system can decrease the beam diameter of a laser beam when the second afocal optical system is moved in a direction from the light beam deflecting device to the transmitter-receiver device. Furthermore, an optical axis of the laser source, an optical axis of the light receiving element and an optical axis of the position detecting sensor in the transmitter-receiver device lie on a first plane, and the first plane is coincident with a second plane including an optical axis of the first afocal optical system and an optical axis of the second afocal optical system.
According to another aspect of the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal and a collimating lens for collimating the laser beam emitted from the laser source, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter, the telescopic optical system including a first afocal optical system; a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor; a second afocal optical system positioned between the light beam deflecting device and the transmitter-receiver device; and a shaping optical system for forming a laser beam collimated by the collimating lens into a predetermined shape in cross section. The first afocal optical system can decrease the beam diameter of a laser beam when the first afocal optical system is moved in a direction from the object side to the light beam deflecting device. The second afocal optical system can decrease the beam diameter of a laser beam when the second afocal optical system is moved in a direction from the light beam deflecting device to the transmitter-receiver device. Furthermore, an optical axis of the light receiving element and an optical axis of the position detecting sensor in the transmitter-receiver device lie on a first plane, and a plane including an optical axis of the laser source and an optical axis of the collimating lens on the one side of the second afocal optical system lies on a second plane which extends parallel to the first plane, the shaping optical system being positioned between the first plane and the second plane. A plane including an optical axis of the first afocal optical system and the optical axis of the second afocal optical system is coincident with the first plane.
According to another aspect of the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source, and for receiving the complementing modulated laser beam transmitted from the complementing transmitter, the telescopic optical system including a first afocal optical system; a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device. The light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor. A second afocal optical system positioned between the light beam deflecting device and the transmitter-receiver device. The first afocal optical system can decrease the beam diameter of a laser beam when the first afocal optical system is moved in a direction from an object side to the light beam deflecting device. The second afocal optical system can decrease the beam diameter of a laser beam when the second afocal optical system is moved in a direction from the light beam deflecting device to the transmitter-receiver device. Furthermore, an optical axis of the laser source, an optical axis of the light receiving element and an optical axis of the position detecting sensor in the transmitter-receiver device lie on a first plane, and the first plane is perpendicular to a second plane including an optical axis of the first afocal optical system and an optical axis of the second afocal optical system.
According to another aspect of the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal and a collimating lens for collimating the laser beam emitted from the laser source, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter, the telescopic optical system including a first afocal optical system; a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor; a second afocal optical system positioned between the light beam deflecting device and the transmitter-receiver device; and a shaping optical system for forming a laser beam collimated by the collimating lens into a predetermined shape in cross section. The first afocal optical system can decrease the beam diameter of a laser beam when the first afocal optical system is moved in a direction from an object side to the light beam deflecting device. The second afocal optical system can decrease the beam diameter of a laser beam when the second afocal optical system is moved in a direction from the light beam deflecting device to the transmitter-receiver device. Furthermore, an optical axis of the light receiving element and an optical axis of the position detecting sensor in the transmitter-receiver device, lie on a first plane. A plane including an optical axis of the laser source and an optical axis of the collimating lens lies on a second plane which extends parallel to the first plane, the shaping optical system being positioned between the first plane and the second plane, and a plane including an optical axis of the first afocal optical system and the optical axis of the second afocal optical system is perpendicular to the first plane.
Preferably, the beam splitting device includes: a central prism; a first auxiliary prism fixed to the central prism by an adhesive; a second auxiliary prism fixed to the central prism by an adhesive; a polarization beam splitting plane, formed on one of two adhesive surfaces between the central prism and one of the first and second auxiliary prisms, for reflecting the modulated laser beam emitted from the laser source towards the light beam deflecting device, wherein the complementing modulated laser beam transmitted from the complementing transmitter can pass through the polarization beam splitting plane; and a beam splitting plane, formed on another of the two adhesive surfaces between the central prism and another of the first and second auxiliary prisms, for splitting the complementing modulated laser beam which has passed through the polarization beam splitting plane into two separate laser beams to be respectively received by the position detecting sensor and the light receiving element.
Preferably, the central prism includes an incomplete right-angled prism having two adhesive surfaces on which the polarization beam splitting plane and the beam splitting plane are respectively provided, the two adhesive surfaces being angled relative to each other by a right angle; wherein the first auxiliary prism is a right-angled prism including: a first adhesive surface adhered to one of the two adhesive surfaces of the central prism on which the polarization beam splitting plane is provided; and a first light incident/exit surface which is angled relative to the first adhesive surface by 45 degrees; wherein the second auxiliary prism is a right-angled prism including: a second adhesive surface adhered to the other of the two adhesive surfaces of the central prism on which the beam splitting plane is provided; and a second light incident/exit surface which is angled relative to the second adhesive surface by 45 degrees.
According to another aspect of the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter; a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor; a collimating lens for collimating the laser beam emitted from the laser source to send the collimated laser beam to the beam splitting device; and a light interceptive member, fixed to the collimating lens, whereby a numerical aperture of the collimating lens smaller than a nominal minimum numerical aperture of the laser source.
Preferably, the light interceptive member is formed so that the numerical aperture of the collimating lens is approximately 80 to 90 percent of the numerical aperture of the laser source.
Preferably, the light interceptive member is integrally formed with a lens holder for holding the collimating lens.
According to another aspect of the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter; a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor; a collimating lens for collimating the laser beam emitted from the laser source to send the collimated laser beam to the beam splitting device; and a light interceptive member, fixed to the collimating lens, for cutting off a peripheral part of the collimated laser beam emitted from the collimating lens.
Preferably, the light interceptive member reduces the quantity of light of the collimated laser beam by approximately 10 to 20 percent.
Preferably, the light interceptive member is formed integral with a lens holder for holding the collimating lens.
According to another aspect of the present invention, there is provided a crosstalk preventive device for an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter; and a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor. The beam splitting device includes: a central prism; a first auxiliary prism fixed to the central prism by an adhesive; a second auxiliary prism fixed to the central prism by an adhesive; a polarization beam splitting plane, formed on one of two adhesive surfaces between the central prism and one of the first and second auxiliary prisms, for reflecting the modulated laser beam emitted from the laser source towards the light beam deflecting device, wherein the complementing modulated laser beam transmitted from the complementing transmitter can pass through the polarization beam splitting plane; a beam splitting plane, formed on another of the two adhesive surfaces between the central prism and another of the first and second auxiliary prisms, for splitting the complementing modulated laser beam which has passed through the polarization beam splitting plane into two separate laser beams to be respectively received by the position detecting sensor and the light receiving element; and a flat surface, formed on the central prism provided between the polarization beam splitting plane and the beam splitting plane extending parallel to a direction of incidence of the complementing modulated laser beam on the beam splitting device, for making the polarization beam splitting plane and the beam splitting plane apart from each other in the direction of incidence.
Preferably, a casing is further provided for accommodating at least the central prism and first and second auxiliary prisms; wherein the casing includes an opening in order for stray light, emitted from the laser source to pass through the polarization beam splitting plane, to exit the casing therethrough.
Preferably, a casing is further provided for accommodating at least the central prism and first and second auxiliary prisms; wherein the casing includes a light interceptive wall, positioned around a border between the polarization beam splitting plane and the beam splitting plane, for preventing stray light from entering one side of the border where the beam splitting plane is positioned from another side of the border where the laser source is positioned.
Preferably, the central prism includes an incomplete right-angled prism having two adhesive surfaces on which the polarization beam splitting plane and the beam splitting plane are respectively positioned, the two adhesive surfaces being angled relative to each other by a right angle, the flat surface of the central prism being angled relative to each of the polarization beam splitting plane and the beam splitting plane by 45 degrees; wherein the first auxiliary prism is a right-angled prism including: a first adhesive surface adhered to one of the two adhesive surfaces of the central prism on which the polarization beam splitting plane is provided; and a first light incident/exit surface which is angled relative to the first adhesive surface by 45 degrees; and the second auxiliary prism is a right-angled prism including: a second adhesive surface adhered to the other of the two adhesive surfaces of the central prism on which the beam splitting plane is positioned; and a second light incident/exit surface which is angled relative to the second adhesive surface by 45 degrees.
According to another aspect of the present invention, there is provided a crosstalk preventive device for an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source, and for receiving the complementing modulated laser beam transmitted from the complementing transmitter; and a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor. The beam splitting device includes: a central prism; a first auxiliary prism fixed to the central prism by an adhesive; a second auxiliary prism fixed to the central prism by an adhesive; a polarization beam splitting plane, formed on one of two adhesive surfaces between the central prism and one of the first and second auxiliary prisms, for reflecting the modulated laser beam emitted from the laser source towards the light beam deflecting device, wherein the complementing modulated laser beam transmitted from the complementing transmitter can pass through the polarization beam splitting plane; and a beam splitting plane, formed on another of the two adhesive surfaces between the central prism and another of the first and second auxiliary prisms, for splitting the complementing modulated laser beam which has passed through the polarization beam splitting plane into two separate laser beams to be respectively received by the position detecting sensor and the light receiving element. Each of light incident/exit surfaces of the central prism and the first and second auxiliary prisms is formed so as not to be parallel to a plane which is angled relative to each of the polarization beam splitting plane and the beam splitting plane by 45 degrees so that reflected light at any of the light incident/exit surfaces of the central prism and the first and second auxiliary prisms cannot enter either the light receiving element or the position detecting sensor.
Preferably, the light incident/exit surfaces of the central prism and the first and second auxiliary prisms are each angled so that an incident laser beam on either the first auxiliary prism or the second auxiliary prism extends parallel or perpendicular to a corresponding emergent laser beam from the central prism, the first auxiliary prism, or the second auxiliary prism.
Preferably, one of the first and second auxiliary prisms, on which the polarization beam splitting plane is provided, includes a first prism which has an isosceles-triangle cross-section having a vertex angle xcex1 of less than 90 degrees; and the other of the first and second auxiliary prism, on which the beam splitting plane is provided, includes a second prism which has an isosceles-triangle cross-section having a vertex angle xcex2 of more than 90 degrees.
Preferably, the sum of the vertex angle xcex1 and the vertex angle xcex2 is 180 degrees.
Preferably, a light exit surface of the central prism, through which a laser beam that is reflected by the beam splitting plane to emerge from the central prism, extends parallel to a surface of at lease one of the first prism and the second prism.
According to another aspect of the present invention, there is provided a crosstalk preventive device for an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device including: a transmitter having a laser source for emitting a laser beam modulated by transmission information signal, a receiver having a position detecting sensor and a light receiving element, each of which receives a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam, which are incident thereon, into two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter; and a light beam deflecting device positioned between the telescopic optical system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor. The beam splitting device includes: a polarizing plate for reflecting the modulated laser beam emitted from the laser source towards the light beam deflecting device, and allowing the complementing modulated laser beam transmitted from the complementing transmitter to pass through the polarizing plate; and a beam splitting plate for splitting the complementing modulated laser beam which has passed through the polarization beam splitting plane into two separate laser beams to be respectively received by the position detecting sensor and the light receiving element.
The present disclosure relates to subject matter contained in Japanese Patent Applications:
No. 10-203765 (filed on Jul. 17, 1998),
No. 10-204549 (filed on Jul. 21, 1998),
No. 10-204550 (filed on Jul. 21, 1998),
No. 10-204552 (filed on Jul. 21, 1998),
No. 10-204553 (filed on Jul. 21, 1998),
No. 10-333828 (filed on Nov. 25, 1998),
No. 10-335826 (filed on Nov. 26, 1998),
No. 11-81312 (filed on Mar. 25, 1999),
No. 11-81344 (filed on Mar. 25, 1999),
No. 11-81446 (filed on Mar. 25, 1999), and
No. 11-81479 (filed on Mar. 25, 1999), which are expressly incorporated herein by reference in their entireties.